OPTICAL RECEIVER

PURPOSE:To attaian stable communication by constituting the title receiver so that the resistance value of an amplifier may be selected according to a light input level, evading the saturation of the amplifier, and to maintain an output voltage pulse width to a prescribed percentage. CONSTITUTION:An optical signal transmitted through an optical fiber is converted into a current corresponding to the level of the optical signal by a light receiving element 1, and converted into a voltage signal V0 by the amplifier and a resistor 3 connected to its input/output. The signal V0 is inputted through a peak value detecting circuit 4 to a first comparing circuit 5a. The circuit 5a inputs the voltage of a reference voltage generating circuit 8a with the suitable output voltage before the saturation of an amplifier 2 as a refeference voltage VB1 beforehand, compares it with the peak value signal, when the peak value signal is larger than the reference voltage VB1, a control signal is outputted to a timer 6. When the control signals are continuously outputted for a prescribed time, the timer 6 operates a relay 7, and drops the resistance value. Thus, the saturation is evaded, and when the signal is larger than a reference voltage VB2, an output voltage VC is outputted through the second comparing circuit 5a. Further, the output voltage pulse width is maintained, for example, to 50%, and the stable communication is attained.